gistfile1.py

class SmartResource(Resource):

    def form_validation_response(self, e):
        """
        Overridden method from piston's Resource class to handle
        form validation errors.
        """
        # Create a 400 status_code response
        resp = rc.BAD_REQUEST

        # Serialize the error.form.errors object
        json_errors = json.dumps(
            dict(
                (k, map(unicode, v))
                for (k,v) in e.form.errors.iteritems()
            )
        )
        resp.write(", " + json_errors)
        return resp